Device for modulating the frequency of electric oscillations



Se t. 6, 1932- B. VAN DER PoL 1,876,109

DEVICE FOR MODULATING THE FREQUENCY OF ELECTRIC OSCILLATIONS Filed NOV. 20, 1929 INVENTOR ammsmz VAN DER POL ATTORN EY oscillations is ensured.

Patented Sept 6, 1932 V UNITED STATES PATENT OFFICE BALTHASAR VAN DER POL, OF EINDHOVEN, NETHERLANDS, ASSIGNOR TO RADIO COR- POBA'IION OF AMERICA, A CORPORATION OF DEI AWARE DEVICE FOR MODULATING THE FREQUENCY OF ELECTRIC OSCILLATIONS Application filed November 20, 1929, Serial No; 408,462, and in the Netherlands November 80, 1928.

This invention relates to light-sensitive cells and more particularly to circuit arrangements in which these cells are used.

In the well known devices these cells areinserted in a circuit in which the current strength varies as the intensity of the light or radiant energy incident on the said cells. In order to obviate the difficulty which is encountered in amplifying these currents, various circuit arrangements have been devised in which modulation of high-frequency oscillations is resorted to.

The invention has for its object to insert the light-sensitive cell or radiant responsive device in a circuit arrangement in such a manner that frequency modulation of electric According to the invention this result is attained by replacing in a circuit, in which relaxation oscillations are set up, the resistance necessary for this purpose or at least part of it with a light-sensitive cell or radiant responsive device.

The invention will be more clearly understood by reference to the accompanying drawing in which the single figure illustrates diagrammatically one embodiment of the invention.

Referring to said drawing a neon tube or glow discharge device 1 is connected in parallel to a condenser 2. A source of direct current or unidirectional potential 3 and a lightsen'sitive cell 4 are connected in series with this parallel connection.

When the current is established by the key 5 being switched into the circuit, the full battery voltage is impressed on the neon tube or glow discharge device 1.

The latter breaks down and the condenser is thus substantially short circuited. In consequence of ionisation by collision in the neon tube the current in the circuit increases and thus the potential drop across the light-sensitive cell 4 increases to such an extent that the voltage across the terminals of the neon tube 1 falls below the operating voltage. The discharge ceases, the short-circuit of the condenser 2 is cancelled and the latter gets charged up until the breakdown voltage 0 the neon tube or glow device 1 is attamed,

after which the operation described is repeated.

The frequency of the oscillations occurring at the terminals of the resistance 6, which are termed relaxation oscillations, is dependent upon the value of the condenser 2 and of the resistance of the light-sensitive cell 4. whose resistance is made to vary in accordance with signals or intelligence to be transmitted. When light variations are applied to the light-sensitive cell 4, the resistance of the cell will undergo variations and the frequency of the relaxation oscillations is consequently modulated correspondingly to the said light variations. i

I claim:

1. In a system for transmitting intelligence by undulatory electrical currents operated upon in accordance with intelligence to be transmitted, a glow discharge device and a resistance in series, a condenser connected across the glow discharge device and the resistance, a source of potential, and a radiant responsive device connected in series with said glow discharge device and said resistance whereby variations in radiant energy falling upon said radiant responsive device causes variations in frequency of oscillations set up between the glow device and said resistance and condenser.

2. In a system for transmitting intelligence'by undulatory electrical currents whose frequency is varied in accordance with the intelligence to be transmitted, a glow discharge device, a resistance in series therewith, a condenser across said glow device and resistance, means for connecting an output circuit across said resistance, and, a source of potential and a radiant responsive device in series, connected across said condenser whereby variations in radiant energy falling upon said radiant responsive device varies the resistance thereof and consequently the frequency of oscillations set up between said glow device and condenser.

3. In a system for transmitting intelligence by varying the frequency of undulatory electrical currents in accordance with the inf 'telligence to be transmitted, a neon glow tube, a resistance in series therewith, a vari- 

